The present invention relates, in general, to a fiber optic-type shock wave sensor which automatically adapts in response to vibrations to prevent generation of false shock wave detection signals.
Pressure sensors are known in the art which are based on the microbend light modulation principle by which the light transmitting characteristics of a fiber optic are detectably changed when the fiber optic is bent by pressure. Typically, this type of pressure sensor employs a mating pair of toothed elements which are movable relative to one another in response to pressure. A fiber optic is positioned between the teeth of the elements so that pressure induced movement of the elements toward each other will cause their teeth to bend the fiber optic, thereby changing its light transmission characteristics. By employing detection circuitry which monitors the light transmission characteristics of the fiber optic, a pressure pulse or shock wave can therefore either be detected or measured by the sensor. Examples of these types of sensors are illustrated in U.S. Pat. Nos. 4,421,979, 4,436,995, 4,770,047, 4,800,267 and 4,860,586.
A problem with fiber optic pressure or shock wave sensors is that they can be adversely effected by vibration. For example, if the sensor is exposed to a vibration which causes the toothed elements to go into resonance, a false detection of a pressure pulse or shock wave may be generated. Conversely, vibration induced resonance of the sensor elements can also prevent a sensor from accurately detecting a pressure pulse or shock wave.
The foregoing considerations are therefore of particular importance when a fiber optic pressure or shock wave sensor is employed in a high vibration environment. For example, this type of sensor can be very useful on an aircraft for detecting shock waves caused by explosions on or around the aircraft. The sensor can be employed in an on board system which generates a signal in response to an explosion that precedes the effect of the explosion on the main airborne system, and can be used as a command for triggering various devices on the aircraft. Unfortunately, there are many sources of vibration on an airborne aircraft, and any shock wave sensor employed in this environment has to be made insensitive to these vibrations without sacrificing the sensitivity of the sensor to shock waves.